Territoriality   (problem name: stake.X)

Farmer John's N (1 <= N <= 500) cows have recently become a bit
territorial in a strange sort of way.  The cows share a large square
field that can be thought of as comprising N rows and N columns.
The strange part is that FJ's cows refuse to share a row or column
with another cow.  FJ must find a way to place the cows in the field
so that as many cows as possible are present, but so that no two cows
are in the same row or column.

To make matters worse, some of the field is bare rock, unsuitable
for grazing.  FJ cannot place cows there.

FJ has been moving cows around all day but still has not found an
arrangement that makes them all happy. In fact, Farmer John is unsure
of _how many_ cows he can make happy: the cows and Farmer John
are all getting a little frustrated with the process.

Help Farmer John find the number of cows that can be placed on the 
field, so that FJ and the other cows can finally go home and watch
their favorite daytime TV show, _As The Grass Grows_... .

PROBLEM NAME: stake

INPUT FORMAT:

* Line 1: A single integer, N

* Lines 2..N+1: N lines describing where the field is bare rock.  Each
        line contains N space-separated 1's and 0's describing a
        single row of the field. A 1 indicates a grassy area, while a
        0 indicates rock.

SAMPLE INPUT:

4
1 0 1 1
0 1 0 0
0 0 0 1
0 1 0 1

OUTPUT FORMAT:

* Line 1: output the largest number of cows that can be placed on the field

SAMPLE OUTPUT:

3